APL DSD-S digital converter

Comparatively little known outside its native Bulgaria, APL Hi-Fi, Ltd has actually been around since 1988. The company’s chief designer, Alex Peychev, exploits his decades working in professional and broadcast electronics to create a comprehensive line of audio equipment, spanning digital front-ends, phono stages, amplifiers, and even loudspeakers. APL is also no stranger to either hollow or solid-state technology, with designs that include both valve and transistor devices.

We focused on APL’s digital side and the middle of three DACs made by the company: the DSD-S from the company’s ‘Illumi-Fi’ series. This is a more full-function converter than the USB only, 24/192 DAC-X (currently the only product in API’s ‘Hi-Fi’ range) but lacking the tube output stage and the considerably higher price of the ‘Illumi-Fi Reference’ DSD-M digital converter. I’ve not had chance to audition either of the other DACs in the APL range, but the smart money from those in the know is thet the DSD-S is in something of a sweet spot in the line.

This is a carriage-built design, truly boutique in outlook and handmade to order: an ambitious concept when it comes to making a DSD-based DAC, because that usually requires a lot of engineering teams. But that’s not the case here; it really is bespoke. Open the player up and you are met with six separate APL-designed PCBs: power supply filtration, power distribution, input block, digital conversion, output block, and display. The digital input block sports the popular XMOS transceiver for USB and some useful crystal clocking circuitry, but the real story on the inside is the use of some classic components inside both the DAC and output stages. The DAC itself is made up of a quartet of Cirrus Logic DSD-chummy chips that are no longer available.

This DAC is controlled by custom code written into an FPGA. Similarly, in the output stage board, the main output MOSFETs are the highly desirable – and long discontinued – Toshiba designs. These are some of the best sounding output devices ever made, and are still used today by companies like Constellation Audio because nothing made this millennia comes close. The board also sports two classic Lundahl coupling transformers, and the closer you get to the output stage, the more the PCBs move from surface mount devices to classic hand-soldered resistors, capacitors, and transistors. It’s not all pre-millennial technology though; alongside that USB input, there are special relay-controlled DC servos in the actual amp stage. Nevertheless, this is a DAC built by someone who knows his way around quality components.